This invention relates to a current-feeding cathode-mounting device, particularly for cathodes for use in refining copper.
Various designs for cathodes for the electrolytic refining of copper are known. Said designs differ as regards the materials or material combinations selected in order to ensure a high electrical conductivity so as to minimize energy losses, and a high mechanical stability so as to reduce repair costs and to minimize production and quality losses, and as regards resistance to corrosion. Owing to its high electrical conductivity, copper has generally been employed as a material for the carrying rails to which, e.g., permanent cathode plates are secured. The carrying rails rest at their ends on busbars, which extend on opposite sides of an electrolytic cell. But copper has disadvantages in that it has only a relatively low strength with regard to damage by deformation during operation and has only a moderate resistance to corrosion, e.g., by the copper-refining electrolyte. In order to improve the resistance to corrosion, the carriers of copper used, e.g., in electrolytic winning processes, have been protected entirely by a sheet metal sheath, which extends as far as to the contact point (bearing point on busbar), and which for reasons of consistency must be joined by a homogeneous soldered joint so that the process is generally uneconomical for electrolytic refining processes.
Laid-open German Application No. 24 34 214 discloses a hanger rail, e.g., of copper, for permanent cathodes, that rail being sheathed with a valve metal by co-extrusion. The sheath metal consists particularly of titanium. The titanium sheath has been removed at the ends of the carrying rail adjacent to the points where it contacts the busbar. A permanent cathode plate consisting of titanium is joined along one edge to the carrying rail by spot welding. Disadvantages are also involved in the use of continuous titanium cathodes of the known type. The process of manufacturing the titanium-sheathed solid copper sections by co-extrusion is highly expensive so that such profiles are used only in special cases and the number of cathodes is usually not very high. Besides, the plate surface which is effective in the process is appreciably passivated by oxidation.
Whereas it would be desirable to combine a titanium-sheathed carrying rail of copper with a cathode plate of corrosion-resisting special steel, that combination cannot be adopted because the materials cannot be joined by welding For this reason Laid-open German Application No. 30 03 927 discloses for use in the electrolytic refining of copper, a hanger rail of stainless steel together with a permanent cathode, which consists also of stainless steel and has been joined by welding. In the known device the hanger rail is provided with a copper covering and a copper covering is also provided adjacent to the point where the cathode plate is welded. It has been found that electro-deposited copper coverings are not satisfactory. The thickness of the required copper covering is highly in excess of the thickness in which copper can generally be electro-deposited (in the micrometer range). The covering must have a thickness of 1.3 to 2.5 mm if appreciable power losses due to voltage drops are to be eliminated and the removal of material by corrosion is to be allowed for. For this reason the copper covering must be applied in expensive special plants, which perform the operations of sand-blasting, cleaning, etching, nickel-plating and copper-plating.
A wide use of the known device is opposed by the technical difficulties and by the high capital requirement for the manufacture of the sheathed solid sections of the carrying rail by coextrusion.